BLAKE RICHARDS, University of TorontoTitle: Systems consolidation and forgetting - the benefits of easily forgotten memoriesEbbinghaus Empire Series 2017-2018

Abstract: It is well established that recent and remote memories can have distinct neurological substrates. For many types of memory, recent memories are more dependent on the hippocampus while remote memories are more dependent on the neocortex. Moreover, it has been shown that as memories become remote they are transformed from a more detailed representation to something more schematic, which can be useful for generalization. The process by which memory substrates and content change over time is known as systems consolidation. The term "consolidation" denotes a process whereby memories are rendered less susceptible to forgetting, so it is interesting to note then, that the hippocampus has several biological mechanisms that seem to promote forgetting, including neurogenesis and spine motility. I have previously argued that forgetting may be promoted by the brain because it can enhance behavioural flexibility. If so, systems consolidation should render animals less flexible, as their memories become less susceptible to forgetting. To test this idea, we trained mice on a probabilistic Y-maze task, then changed the rules of the task 1 day or 28 days after they reached threshold. We find that mice are worse at adapting to the new rules 28 days after than 1 day after training. Immediate early gene data supports the idea that at 1 day the animals are relying on their hippocampus more, and at 28 days they are relying on their neocortex more. Taken together with past results, these data suggest that recent, hippocampus-dependent memories are more likely to be forgotten, which may actually benefit an animal by making it easier for them to adapt to changes in the environment.

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